1. Field of the Invention
The present invention relates generally to a routing device for connecting multiple physically discrete networks into a single system.
2. Description of the Related Art
Recently various home networks connecting multiple electronic devices over a network have been introduced. The devices connected to these home networks are generally low-cost home appliances for which high reliability operation is required. The devices connected to such home networks enable the network to be used for a variety of applications, including security systems and remote control systems.
FIG. 1 is a schematic diagram of a typical home network. As shown in FIG. 1 a refrigerator 1, a washing machine 2, an air conditioner 3, a television 4, a controller 11, and so on are connected to a powerline communication network 15. A microwave 5, a bath (hot water heater) 6, a gas range 7, and so on are connected to a wireless communication network 16. A sleep sensor 8, an entry sensor 9, a telephone 10 and so on are connected to a dedicated line 14. The powerline communication network 15 and the dedicated line 14 are connected to a router 12, and the powerline communication network 15 and the wireless communication network 16 are connected to a router 13. These network connections complete the in-home network.
Other devices that might also be connected to this network include lighting fixtures and other home appliances. Infrared and other transmission media could also be used in addition to or instead of electrical power lines, wireless transmission, and dedicated lines. Multiple controllers for specific services could also be used instead of using a single controller as shown in FIG. 1.
FIG. 2 is a system diagram showing the conceptual arrangement of devices and routers connected to this home network. As shown in FIG. 2 a subnet A 21 is connected to a subnet B 22 through a router 31 and to a subnet C 23 through a router 32. Network devices 21a to 23d are connected to subnets 21 to 23. The routers 31 and 32 could be any device that functions as a router. Various standards and concepts have been proposed for effectively running and using such networks. These include, for example, ET-2010 and ECHONET Specification Ver.1.00, proposed by the Electronic Industries Association of Japan (EIAJ) and the ECHONET Consortium.
Assume, for example, that the router 31 shown in FIG. 2 is operating and network device 21a functions as a router (“parent router” below) that assigns “Net ID” as a subnet identifier. If a new router 32 is then added to the system, the router 32 must first start up as a network device 21c and 23d recognizable by subnet 21 and subnet 23, respectively, and must then query subnet 21 and subnet 23 to determine if a router already exists on the respective subnets. If a router is found on each subnet, the router 32 starts up as a network device of both subnets without activating its functionality as a router.
If on at least one (21) of the plural subnets (21 and 23) there is a router (31) and on at least one (23) of the subnets there is no router, the router 32 queries the detected router to acquire data about the parent router (i.e. network device 21a in this example). The router 32 then requests the parent router (network device 21a) for the information required for the router 32 to function (i.e., a router identifier and Net ID for the new subnet added to the system), and based on this router information obtained from the parent router (network device 21a) passes the Net ID to all network devices 23a to 23c on the subnet 23 to which a new Net ID was allocated.
The Net IDs uniquely allocated as subnet identifiers and the node ID numbers allocated as identifiers uniquely identifying each device on a particular subnet enable each device to be uniquely addressed within the overall system formed by linking plural subnets via routers.
Conventional network methods and routers function adequately when the routers start up in the same order previously used. Problems such as those described below occur, however, if Net IDs are already assigned to the subnets by the router (that is, the same Net ID is allocated to all network devices connected to a particular subnet), since all network devices on the subnet use the assigned Net ID to exchange data with other devices in the domain, if, for example, the power supply suddenly shuts down due to a power outage, then a system-wide reset occurs.
If the subnet identifiers (i.e., Net IDs) are assigned in the sequence that the routers start up in a system having three or more subnets, a subnet identifier (Net ID), that is different from the subnet identifier assigned before the reset, could be assigned when the system resets depending upon the startup sequence of the routers. If in the network configuration shown in FIG. 2, for example, the router 31 starts up first and is therefore assigned a Net ID identifying subnet B, the router 32 then starts up and is assigned a Net ID identifying subnet C, when due to a power failure the system restarts and the router 32 starts up first and the router 31 then restarts, the router 32 will be set as subnet B and router 31 will be set as subnet C. In other words, Net IDs assigned to the routers may change when the system resets due to the power outage.
Furthermore, if only one of the routers in the system resets or is replaced and there is another router on any of the subnets to which the reset or replaced router belongs, the reset or replaced router will start up simply as a network device other than the router on the subnets and its router function will not restart.
This can result in excessive time being required for the overall system to restart when a short-term power outage occurs on a home network, and the controllers and user could be confused by device identifiers that differ before and after the power outage, thus necessitating a service call by a trained technician.
Replacing a router is also not a simple task. The user (i.e., a typical homeowner) must acquire the subnet data for the subnet(s) formed by the router connection before replacing the router by, for example, connecting a display to the router to display the information, and must then reset the same information to the replacement router by setting switches, for example. The need for a person to intervene to make these settings introduces the potential for setup errors which can then prevent the system from functioning normally.
A problem with the router and router startup procedure according to the prior art as described above is that when there is another router on any of the subnets to which a router that is replaced or reset belongs and a Net ID is already assigned to those subnets, the replaced or reset router does not function as a router but simply as another network device. Communication with the subnets that should be connected by the replaced or reset router is thus not possible.
A further problem with the router and router startup procedure according to the prior art as described above is that while a router that is replaced or reset (referred to below as the “target router”) will function as a router when there is another router on one or more of the subnets to which the target router connects but there is not a router on a different one or more such subnets, the parent router allocates a new Net ID to the subnet that does not have a router. The Net ID may thus be different before and after the router is replaced or reset, and the parent router, subnet router, and network devices use a different Net ID to uniquely identify each network device on the subnet within the network system. As a result, network devices on another subnet that had been communicating with network devices on the subnet for which the router was replaced or reset before the router was replaced or reset are unable to recognize that the network device identification information (Net ID) changed, and an error results when communication is next attempted because the addressed network device cannot be found on the network.
A further problem with the router and router startup procedure according to the prior art as described above occurs. That is, if communication with the parent router is not possible because there is another router on one or more subnets to which the target router that is replaced or reset connects and there is not a router on another one or more subnets, or because, even though there is a router operable to start up as a router, the parent router is separated via several subnets from the target router but there is a malfunctioning router somewhere between the target router and the parent router, then the target router cannot activate its router function and can only startup as another non-router network device. Communication between network devices on subnets previously connected by the target router is also disabled until the entire system resets.